1. Field of Invention
The present invention relates to access plug flanges for inspection ports in processing equipment insulation.
2. Description of Prior Art
In chemical processing, container and pipe walls are typically covered with foam coatings or other insulation materials inside jackets or covers for thermal insulation. For various reasons including safety and environmental concern, periodic inspections of the vessel and pipe walls must be performed. Access through the insulation to the vessel or pipe wall has been provided through pre-cut or drilled inspection holes or ports formed in the jacket and insulation coating. It has been the practice for protection against moisture and weather conditions to have the inspection ports normally sealed with plugs. For this reason, it has been customary to mount access flanges in the inspection holes to receive sealing plugs.
An example of this type equipment is that of U.S. Pat. No. 4,091,842. The access flanges were closed by the sealing plugs during normal service conditions. The plugs were intended to be removable when wall inspections or tests were required. However, there were problems.
If the plugs were easily removable, they often did not effectively seal the inspection port against weather and moisture. If the plug were lost, water contact with certain types of insulation materials produced a chlorine effect which with some grades of stainless steel vessels resulted in premature failure due to embrittlement. If the plugs sealed too tightly, they often could not be removed without damaging the flange connection with the insulation and jacket. It was not unusual for the plug to be so tightly fitted in the flange that when the plug was pulled, the entire flange assembly pulled free along with portions of the insulative cover. Other problems with prior art access plugs and flanges have included the requirement for expensive, special purpose installation tools and procedures and the possibility of plug loss or separation of the plug from the flange. A vessel surface exposed to moisture due to a lost or misplaced plug was unacceptable because of leakage or hazardous emissions.